We determined whether neural responses to
inflammation and
hyperalgesia involve activation of
kainate receptors, a subgroup of
glutamate receptors.
Inflammation was introduced into the hind paw by intraplantar injection of complete
Freund's adjuvant. The
inflammation-induced
thermal hyperalgesia was attenuated by intrathecal administration of a non-selective
alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (
AMPA)/
kainate receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-
benzo[f]quinoxaline-7-
sulfonamide disodium (
NBQX), as well as by selective
kainate receptor antagonists, 6,7,8,9-tetrohydro-5-nitro-1H-benz[g]
indole-2,3-dione 3-oxime (NS-102) and 3S,4aR,6S,8aR-6-(4-carboxyphenyl)methyl-1,2,3,4,4a,5,6,7,8,8a-deca-hydroisoquinoline-3-carboxylic
acid (
LY382884). Reverse transcription-polymerase chain reaction (RT-PCR) indicated that the GluR5 and GluR6, but not the GluR7, KA1 and KA2 subunits, exhibited increased
mRNA expression at 2 h to 3 days following
inflammation (P<0.05). Western blot showed an increase in GluR6
protein levels (P<0.01) with a time course consistent with the changes in its
mRNA levels.
cDNA sequence and
BbvI endonuclease digestion of the GluR6 PCR product revealed that the upregulated GluR6 mRNAs were predominantly the unedited form (Q). These results suggest that a selective upregulation of
kainate receptor subunit expression contributes to inflammatory
hyperalgesia.